Containment of dust and fumes from a metallurgical vessel

ABSTRACT

A device for use with the exhaust hood of a metallurgical furnace to improve its ability to capture waste gas effluent escaping from the furnace especially when the mouth of the furnace is rotated away from the mouth of the hood for tapping or charging comprises a pair of parallel tracks that are mounted adjacent to the hood and that straddle the mouth of the hood and extend beyond it, a movable closure plate for partially closing and restricting the cross-sectional area of the mouth of the hood that is carried by the tracks and means for moving the closure plate from a position remote from the mouth of the hood to a position adjacent to and partially restricting the crosssectional area of the mouth of the hood. When the closure plate partially restricts the cross-sectional area of the mouth of the hood there will be an increase in the face velocity, thus drawing the effluent through the unrestricted cross-sectional area of the mouth of the hood so that the effluent from the furnace will be captured and drawn into the hood.

United States Patent 1191 Gaw 1 1 Dec. 17, 1974 Richard Gerard Gaw,Pittsburgh, Pa.

[73] Assignee: Mary F. Gaw, Pittsburgh, Pa. a

part interest 22 Filed: July 13, 1973 21 Appl.No.: 379,l63

[75] Inventor:

4/1963 Germany 122/7 A 1,099,284 9/1955 France 110/173 A PrimaryExaminer-Gerald A. Dost Attorney, Agent, or FirmFred C. Trenor, Esq

[5 7 ABSTRACT A device for use with the exhaust hood of a metallurgicalfurnace to improve its ability to capture waste gas effluent escapingfrom the furnace especially when the mouth of the furnace is rotatedaway from the mouth of the hood for tapping or charging comprises a pairof parallel tracks that are mounted adjacent to the hood and thatstraddle the mouth of the hood and extend beyond it, a movable closureplate for partially closing and restricting the cross-sectional area ofthe mouth of the hood that is carried by the tracks and means for movingthe closure plate from a position remote from the mouth of the hood to aposition adjacent to and partially restricting the cross-sectional areaof the mouth of the hood. When the closure plate partially restricts thecross-sectional area of the mouth of the hood there will be an increasein the face velocity, thus drawing the effluent through the unrestrictedcross-sectional area of the mouth of the hood so that the effluent fromthe furnace will be captured and drawn into the hood.

21 Claims, 7 Drawing Figures PAIENIL, ifLCI H974 sum 1- or 5 CONTAINMENTOF DUST AND FUMES FROM A METALLURGICAL VESSEL BACKGROUND OF THEINVENTION A. Field of the Invention This invention relates to thecontainment of waste gas effluent from a metallurgical furnace and tothe exhaust hoods of such furnaces and, more particularly, to a deviceto capture fugitive plume escaping from such furnace especially when themouth of the furnace is rotated from the mouth of the hood so that othermetallurgical operations can be performed on the furnace, such as, forexample, the charging of raw materials into the furnace or the tappingof molten metal from the furnace.

The exhaust hood for metallurgical furnaces particularly for the basicoxygen furnace (BOF) receives and conducts the waste gas effluentgenerated in the furnace away from the furnace to a gas cleaningapparatus remote from the furnace. When oxygen is introduced into abasic oxygen fumaceduring the steel refining process or blowing period,large quantities of waste gas effluent are produced by the chemicalreaction of gaseous oxygen with the hot molten metal in the furnace; itis not at all unusual for the effluent to reach temperatures of 3,500For even higher. The duration of the steel refining process or theduration of the blowing period the gaseous oxygen into the molten metalis usually from twenty to twenty-two minutes and the quantity of wastegas effluent discharged during that period of time is of the order of 50cubic feet per minute or more per cubic foot of oxygen blown.

Accordingly, the exhaust hood of BOF furnaces while they may be simplein concept are rather complicated pieces of equipment requiringconsiderable protective measures such as water cooling and/or refractorybrick to protect the hood and its structure from the hot, abrasive wastegas effluent from such furnaces. Most hood systems efficiently. andeffectively contain the effluent from the furnace during the steelrefining period which are subsequently treated so that there is noappreciable pollution of the surrounding, environment during that periodof time.

In the case of BOF furnaces, the furnace is usually in its verticalposition during the steel refining process but is rotated from thisvertical position to receive scrap and hot metal ingredients on one sidefor charging and rotated in the opposite direction from this position todischarge molten metal for tapping after the steel retining period. Atthese out-of-vertical positions, there is considerable misalignment ofthe mouths of the furnace and the hood, thus, reducing the effectivenessof the hood in capturing the effluent. B. Description of the Prior ArtHeretofore, the primary concern has been with the containment of thewaste gas effluent generated during the steel refining period or theblowing period of the BOF while the waste gas effluent generated duringthe tapping and charging periods has been merely ignored and tolerated.However, with the advent of stricter air pollution emission standards,it has been necessary to devise and consider supplementary andauxilliary devices to contain and recover the waste gas effluent duringthese periods of operation.

Several proposals have been made, many of which are inefficient,uneconomical and unsuitable for the task. For example, it has beensuggested to operate the hood system at its capacity to contain thewaste gas effluent generated during charging and tapping periods. Thedifficulty with this proposal is that ambient air would be evacuated inpreference to the waste gas effluents by the hood and, accordingly, theeffluents would be liberated into the surrounding environment.

It has been suggested to use supplementary devices installing them atexisting operations. Such supplementary devices usually compriseauxilliary hoods that are mounted adjacent to existing hoods to containthe ef fluent generated during charging and tapping. In some cases suchauxilliary hoods include their own evacuating and gas cleaning equipmentseparate from the regular hood evacuation system. Obviously, suchalternatives are an economic burden to the process. In some plants, thephysical layout of the plant precludes the use of supplementary devicesand, accordingly, other impractical alternatives must be sought.

None of the foregoing solutions proposed to the art have beensatisfactory and, accordingly, there has been a long-felt need for adevice that utilizes existing hood systems and gas cleaning systems tocapture and clean the fugitive'waste gas effluent generated during thetapping or charging operations of the process without becoming aneconomic burden to the process.

SUMMARY OF THE INVENTION In accordance with the invention, a device foruse with the exhaust hood of a metallurgical furnace to improve thewaste gas effluent capture efficiency of the hood in exhausting effluentfrom the furnace comprises closure means for partially restricting thecrosssectional area of the mouth of the hood to increase the facevelocity of gas effluent passing through the mouth thereof, supportmeans fixed adjacent to the hood for carrying the closure means anddrive means for moving the closure means from a position that is remotefrom the mouth of the hood to a position that is adjacent to the mouthof the hood to restrict the cross-sectional area of the mouth of thehood so that fugitive waste gas effluent is captured by and passesthrough the unrestricted cross-sectional area of the mouth of the hood.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a side elevational view illustrating an embodiment of theinvention in conjunction with a basic oxygen furnace and its cooperatinghood wherein the basic oxygen furnace is illustrated in phantom lines inan upright position and in solid lines in a tapping position from theupright position;

FIG. 2 is a side elevational view illustrating the embodiment of FIG. 1wherein the basic oxygen furnace is illustrated in phantom lines in anupright position and in solid lines in a charging position from thevertical;

FIG. 3 is a front elevational view of the embodiment of FIG. 1 taken atline III-III of FIG. 1;

FIG. 4 is a top plan view of the embodiment of FIG. 1 taken at lineIV-IV at FIG. 1;

FIG. 5 is a top plan view of the embodiment of FIG. 2 taken at line VVof FIG. 2;

FIG. 6 is a top plan view of another embodiment of the invention; and

FIG. 7 is a top plan view of still another embodiment of the invention.

DETAILED DESCRIPTION In FIG. 1 there is illustrated a basic oxygenfurnace 11 and its cooperating hood 13 with an embodiment of theinvention generally indicated at 15. The furnace 11 is illustrated inphantom lines in its upright position, the normal position in which thefurnace resides during the steel refining process or the oxygen blowingperiod, and the furnace is also illustrated in solid lines in itstapping position, being rotated from the vertical position. In contrast,the furnace 11 in FIG. 2 is also illustrated in phantom lines in anupright position and is illustrated in solid lines in its chargingposition, being rotated from a vertical position opposite the furnacetapping position shown in FIG. 1.

The embodiment of the invention generally indicated at 15 includes apair of parallel tracks 17 lying in a common plane, a movable closureplate 19 carried by thetracks and driving means 21 for moving theclosure plate from a position remote from the hood to a positionpartially restricting the cross-sectional area of the mouth of the hood.

The furnace 11 illustrated in the drawings is a typical basic oxygenfurnace although the particulars of its design and construction are notillustrated in the drawings and are not critical to the invention.

The hood 13 illustrated in the drawings is a typical water-cooled hoodalthough the particulars of its design and construction are notillustrated in the drawings and are not critical to the invention.

The tracks 17 are mounted on or adjacent to the hood 13. As illustratedin FIG. 3, there are two tracks straddling the hood 13 beingsubstantially parallel to each other and lying in a common plane. Asshown in FIGS. 1 and 2 each track-extends beyond the hood so that theclosure plate 19 may reside in a remote position from the hood (PositionA in the drawings) during the steel refining process but in an engagedposition (Position B in FIG. 1 for tapping) and (Position C in FIG. 2for charging). Each track 17 is secured adjacent to the hood 13 byexpansion mechanisms 23 which, in turn,-are secured to frame 25, a partof the building structure 27 independent of the hood. Each track isillustrated as being secured to three expansion mechanisms 23(a), (b)and although more or less of such mechanisms may be used.

Each expansion mechanism 23 comprises a hydraulically driven,pneumatically-driven or screw-driven cylinder that is capable of movingin a vertical direction so that the tracks 17 and the closure plate 19may be raised or lowered with respect to the mouth 29 of the hood 13.Each expansion mechanism 23 is synchronized for movement with each otherso that both tracks may be uniformly raised or lowered as desired. Thepurpose of the expansion mechanism is to adjust the position of thetracks with respect to the hood and in turn the position of the closureplate with respect to the mouth 29 of the hood as thermal expansion andconv traction of the hood is experienced. The maximum expansion andcontraction experienced in the hood is about seven inches depending uponthermal conditions.

Expansion mechanisms 23 are only necessary on those hoods 13 that aresupported from the top and that are permitted to hang in suspension andexpand thermally from this fixed point, the type intended to beillustrated in the drawings herein. Expansion mechanisms 23 would not benecessary were the hood supported at the mouth level and permitted toexpand thermally upwardly from the mouth level. The use of the expansionmechanism is a desirable feature of the invention since the closureplate 19 must be in close proximity to the mouth 29 of the hood so as toreduce the volume of ambient air drawn into the hood system when theclosure plate is in the partially closed position restricting thecross-sectional area of the hood.

Each track 17 has generally a closed face 33 facing the mouth of thehood to protect the tracks from the accumulation of molten metal and thelike and is further protected with a heat shield 31 as best illustratedin FIG. 3. The purpose of the heat shield is to protect the track fromexposure to the high temperatures that occur near and about the mouth ofthe hood and further to protect the tracks from amounts of molten metalthat might inadvertently splash onto the tracks from the furnace 11 andthus interfere with the travel of the closure plate along the tracks.

The closure plate 19 as illustrated in the drawings is cooled with afluid, such as, for example, water. In the drawings, the hood has waterinlet and outlet means 35(a) and (b) that are connected to flexiblehoses (not shown) and in turn to a source of water (not shown) for thepurpose of cooling the plate from the high tempera- ,tures generatednear and aboutthe mouth of the hood.

The manner of construction of the closure plate 19 is not essential tothe invention so long as it is capable of withstanding high temperaturesgenerated near and about the mouth of the hood. Alternatively, theclosure plate may be protectedwith refractory bricks.

The closure plate 19 is generally rectangular having a planerconstruction and is secured to brackets 37 that are mounted near theedge of the plate as shown in FIG. 3. The brackets 37 are joumalled towheels 39 that are adapted to freely rotate on the tracks 17 asillustrated. Each wheel 39 has a peripheral groove 41 in the center ofits periphery cooperating with the lips 43 of the track thereby securelyholding the closure plate and the wheel with respect to the track. Itwill be recognized that while this embodiment of the wheels 39 ispreferred, other embodiments may be used in accordance with theinvention. Accordingly, the closure plate 19 is capable of free movementto and along the track 17 from a remote position (Position A) to aposition in partial closure of the mouth 29 of the hood (Position B orPosition C as illustrated in the drawings).

In all of the drawings except FIGS. 6 and 7, one embodiment of thedriving means 21 is illustrated. As best observed in FIG. 3 there aretwo driving means, one mounted on each side of the closure plate. Theclosure plate 19 acts as a heat shield to protect the driving means fromthe intense heat resulting from the tapping and charging of the furnacewhen the closure plate is in either one of the two engaged positions. InFIGS. 1 through 5 each driving means 21 comprises a motor 45 driving adrive wheel 47. Drive wheel 47 engages the tracks 17 as illustrated inFIG. 1. The motor 45 is capable of forward and reverse drive andappropriate controls for the motor 45 and its directionality are mountedin the operator's station (not shown). The

movement of each motor is synchronized with the other motor so that theclosure plate smoothly moves from its remote position to either one ofits engaged positions. Preferably, electrical motors are used but it isapparent that other kinds of motors may be used in the practice of theinvention without limitation.

In FIG. 6, on the other hand, there is illustrated another embodiment ofthe driving means that may be used in accordance with the invention. Thedriving means comprises one motor 49 mounted to the frame at the remoteend of and between the tracks 17. Drive axle 51 extends between thetracks and is driven by the motor; the drive axle is journalled at bothof its ends to a drive sprocket wheel 53. Each sprocket wheel 53 drivesa chain 55, one on each side in alignment with the tracks, that extendsalong the length of the tracks from the remote end to the opposite endof the tracks. At the other end of the tracks, there is a secondsprocket wheel 57 for carrying the chain 55. On each side of the closureplate 19 there is mounted a cog wheel 56 engaging the chain 55 so thatas the chain is advanced the closure plate is moved. Motor 49 is capableof forward and reverse drive and appropriate controls for the motor aremounted in the operators station (not illustrated in the drawings).Preferably, an electrical motor is used but it is apparent that otherkinds of motors might be used in the practice of the embodiment of thisinvention without limitation.

In FIG. 7, there is illustrated still another embodiment of the drivingmeans that may be used in accordance with the invention. The drivingmeans comprises two hydraulically or pneumatically driven cylinders 59that are pivotedly mounted to the frame at 60 at the remote end of thetracks 17. The pivotal mount at 60 is necessary to accommodate thevertical movement of the tracks by the expansion mechanisms 23. Eachcylinder 59 carries a plunger rod 61 that is pivotedly mounted at 62 tothe closure plate 19 as illustrated in FIG. 7. Again, the pivotal mountat 62 is necessary to accommodate the vertical movement of the tracks bythe expansion mechanisms 23. When the plunger rod 61 of each cylinder isextended, the closure plate is moved from the remote position (PositionA) to either position adjacent the hood of the mouth as shown in FIG. 7;When the plunger rod is retracted, the closure plate is returned to itsremote position. Appropriate controls for the cylinders are mounted inthe operators station (not shown in the drawings). It will be observedthat in applications where there is a long travel distance, compoundplunger rods may be necessary.

As illustrated most clearly in FIGS. 4 and 5, the closure plate 19 hasthree basic positions with respect to the hood that are coordinated withthe three basic positions of the furnace. The three basic positions ofthe closure plate are (a) a retracted or remote position where thefurnace is in a vertical position for the steel refining process andwhere the closure plate is remote from the hood (Position A); (b) atapping position where the furnace is rotated from its vertical positionto the left in FIGS. 1 and 4 and where the closure plate is positionedso that the unrestricted cross-sectional area of the hood is also to theleft in FIGS. 1 and 4 (Position B); (c) a charging position where thefurnace is rotated from its vertical position to the right in FIGS. 2and 5 and where the closure plate is positioned so that the unrestrictedcross-sectional area of the hood is also to the right in FIGS. 2 and 5(Position C). The closure of the mouth 29 of the hood is partial whenthe closure plate is in a position for tapping (Position B) or forcharging (Position C). The amount of closure of the caping plume.

cross-sectional area of the mouth of the hood is proportional to thedistance between the mouths of the hood and furnace or, in other words,proportional to the zero velocity point of the plume escaping from thefurnace as will be explained later. The percentage of closure for anygiven circumstance will depend on the abovestated variables and in eachinstallation, it will be necessary to calculate and determine theoptimum conditions for the containment of the effluent when the furnaceis either being tapped or charged. Preferably, the movement of theclosure plate is synchronized with the movement of the furnace as it isrotated to either a tapping or charging position.

In use, the closure plate is normally maintained at its remote position(PositionA) during the steel refining period when the furnace ismaintained in an upright position (illustrated in phantom lines in thedrawings). Prior to tapping or charging of the furnace, the closureplate 19 is moved to either one of its two engaged positions (Position Bor C). Preferably, the movement of the closure plate is coordinated withthe movement of the furnace, while the closure plate is being moved theavailable draft of the hood is maintained at its normal operatingcondition. As the cross-sectional area of the mouth of the hood isrestricted, the face velocity of ef fluent entering the hood through theunrestricted crosssectional area is increased in proportion to theamount of closure. Once the closure plate reaches its engaged position(either Position B or C), the expansion mechanisms 23 are activated tobring the closure plate into close proximity with the mouth of the hoodto restrict the volume of ambient air that otherwise might be exhaustedinto the hood. With this increased face velocity, the hood is nowcapable of more effectively capturing the effluent escaping from thefurnace and its surroundings. As the furnace is rotated further from theupright position the more face velocity would be needed and accordingly,a greater restriction of the mouth of the hood would be required. Whenthe furnace is to be returned to its upright position, the expansionmechanisms 23 are deactivated lowering the closure plate 19 from themouth of the hood so that the closure plate may easily be returned toits remote position (Position A).

One of the desirable features of the present invention is that it caneasily be installed on present hood systems throughout the industry andtheir existing exhaust systems need not be altered materially. Most ofthe existing exhaust capabilities now existing in the industry aresatisfactory for the successful utilization of the invention. Forexample, many hood systems presently in use have a draft capacity of onemillion cubic feet per minute. Assuming that the diameter of the mouthof the hood is approximately 17 feet, a face velocity at the mouth ofthe hood of 60 feet per second can be achieved. Such a face velocity isnot sufficient to effectively capture effluent when the furnace ismisaligned from the hood. It is generally believed that for a hood toeffectively capture effluent from a furnace that is not aligned with thehoodrequires a face velocity of 200 feet per minute at the zero velocitypoint of the es- The zero velocity point of a plume comprises a locus ofpoints within the plume where there is no movement of gases. It existswhere the gases have a temperature that is no greater than a temperaturethat is equal to ambient temperature plus ten percent (10 perature atthe center of the plume were 800F, then the zero velocity point would bethat locus of points at the zero velocity point of the plume should beabout 200 feet per minute meaning that the face velocity at the mouth ofthe hood must be greater than 200 feet per minute, the actual value ofwhich'will depend on the physical location of the zero velocity point inthe plume.

While the present invention has been described with particular referenceto basic oxygen furnaces, it will be recognized that the invention isapplicable to other types of metallurgical furnaces with but minormodifications.

What is claimed is:

1. A device comprising:

a. a rotatable metallurgical furnace having a furnace mouth disposed atits top; said furnace being dis posed in an upright position for oxygenblowing operations and being adapted to rotate about an axis to the leftand to the right of said upright position for operations other thanoxygen blowing operations;

b. an exhaust hood positioned above said furnace for the capture of gaseffluent; said hood having a hood mouth that is aligned with saidfurnace mouth when said furnace is disposed in said upright position;and

0. means for use at said hood mouth that is capable ofvariably andpartially restricting selected portions of the cross-sectional area ofsaid hood mouth to provide a reduced, unrestricted portion and arestricted portion at said hood mouth; said means being cooperativelyassociated with the rotation of said furnace from its upright positionso that said reduced unrestricted portion is disposed to the left ofsaid restricted portion when said furnace is rotated to the left of saidupright position and said reduced unrestricted portion is disposed tothe right of said restricted portion when said furnace is rotated to theright of said upright position whereby the face velocity of gaseffluents entering said hood through said reduced unrestricted portionis increased to improve the capacity of said hood to capture gaseffluents.

2. The device of claim 1 including means for synchronizing the partialrestriction of said hood mouth with the rotation of said furnace fromits upright position.

3. The device of claim 1 wherein said means comprises a plate.

4. The device of claim 3 wherein said plate is protected from heat.

5. The device of claim 3 wherein said plate is cooled with a fluid.

6. The device of claim 3 wherein said plate iscooled with water.

7. The device of claim 1 wherein said means is external of said hood.

8. The device of claim 1 wherein said means is capable of moving withrespect to the thermal movement of said hood so that the distancebetween said means and said hood is constantly maintained.

9. The device of claim 1 wherein said metallurgical furnace is a basicoxygen furnace.

10. The device of claim 1 wherein said means is capable of partiallyrestricting the cross-sectional area of said hood mouth in proportion tothe degree of rotation of said furnace from its upright position.

11. A device comprising:

a. a rotatable metallurgical furnace having a furnace mouth disposed atits top; said furnace capable of being disposed in an upright positionfor oxygen blowing operations and capable of being rotated about an axisin a plane of rotation in two opposed directions;

b. an exhaust hood positioned above said furnace having a hood mouththat is aligned with said plane of rotation of said furnace;

0. means for use at said hood mouth when said furnace is rotated fromits upright position that is capable of variably and partiallyrestricting selected portions of the cross-sectional area of said hoodmouth to provide a reduced unrestricted portion and a restricted portionat said hood mouth; said reduced unrestricted portion being disposed inthe same direction to which said furnace mouth is rotated and saidrestricted portion being disposed in the opposite direction to whichsaid furnace mouth is rotated, whereby the face velocity of gaseffluents entering said hood through said reduced unrestricted portionis increased to improve the capacity of said hood to capture gaseffluents.

12. A device for improving the gas effluent capture efficiency of anexhaust hood having a hood mouth through which gas effluent is capturedthat is cooperatively associated with a rotatable metallurgical furnacehaving a furnace mouth; said hood mouth and said furnace mouth beingcapable of alignment with each other and being capable of misalignmentwith each other in two opposed directions of misalignment; said devicecomprising;

Means for use at said hood mouth that is capable of variably andpartially restricting selected portions of the cross-sectional area ofsaid hood mouth to provide a reduced unrestricted portion and arestricted portion at said hood mouth and that is capable of providingsaid reduced unrestricted portion nearer said furnace mouth than saidrestricted portion when said furnace mouth is misaligned in eitherdirection if misalignment with said hood mouth whereby the face velocityof gas effluents passing through said reduced unrestricted portion isincreased to improve the gas effluent capture efficiency of said hood.

13. The device of claim 12 including means for synchronizing the partialrestriction of said hood mouth with the degree of misalignment of saidfurnace mouth and said hood mouth.

14. The device of claim 12 wherein said means comprises:

a. a pair of parallel tracks fixed adjacent to said hood lying in acommon plane that extends adjacent to and beyond said hood mouth;

b. a movable plate that is carried by said tracks; and

c. means for moving said plate from a position remote from said hoodmouth to a position adjacent to said hood mouth in partial restrictionthereof.

15. The device of claim 14 wherein said tracks carry means forprotecting said tracks from heat and molten metal.

16. The device of claim 14 wherein said moving means comprises:

a. a pair of motors each of which is mounted on said plate at the sidesthereof; and

b. a drive wheel being carried by each of said tracks being rotatablyfixed to each of said motors for moving said closure plate along saidtracks; each of said motors being synchronized with each other.

17. The device of claim 14 wherein said driving means comprises:

a. a motor situated at the remote end of and between said tracks;

b. a drive axle cooperatively associated with said motor and extendingbetween said tracks;

c. a pair of first sprocket wheels one of which is mounted to one end ofsaid drive axle and the other of which is mounted to the other end ofsaid drive axle;

d. a pair of second sprocket wheels disposed at the other opposite endof said tracks, one of which is cooperatively associated with one ofsaid first sprocket wheels and the other of which is cooperativelyassociated with the other of said first sprocket wheels.

a pair of continuous chains engaging each pair of cooperating first andsecond sprocket wheels; and,

f. a pair of cog wheels fixed to each side of said plate, one of whichis cooperatively associated with one of said continuous chains and theother of which is I cooperatively associated with the other of saidcontinuous chains.

18. The device of claim 14 wherein said driving means comprises:

a. two cylinders each of which is pivotedly mounted to a frame at theremote end of said tracks;

b. each cylinder carrying a plunger rod having its free end pivotedlymounted to said plate; and,

c. means for activating said plunger rods for extension and retraction.

19. The device of claim 14 including expansion mechanisms for movingsaid tracks with respect to said hood mouth to accommodate the thermalexpansion of said hood so that the distance between said plate and saidhood mouth is constantly maintained.

20. The device of claim 19 wherein said expansion mechanisms comprises:

a. a cylinder secured to a frame;

b. each cylinder having a plunger rod that is secured to said tracks;and

c. means for activating said plunger rods for extension and retraction.

21. in an exhaust hood having a hood mouth that cooperates with arotatable metallurgical furnace having a furnace mouth and being adaptedto rotate about an axis in a clockwise and a counter-clockwisedirection; said hood mouth having a centerline perpendicular to theplane in which said hood mouth lies and said furnace mouth having acenterline perpendicular to the plane in which said furnace mouth lies;said centerlines being coaxial when said furnace is disposed in aposition for oxygen blowing operations and said centerlines intersectingeach other at an angle when said furnace is rotated clockwise orcounterclockwise, wherein the improvement comprises:

Means for use at said hood mouth that is capable of moving into aposition adjacent to said hood mouth that partially restricts thecross-sectional area of said hood mouth to provide a reducedunrestricted portion having a centerline that is perpendicular to theplane in which said reduced unrestricted portion lies and that issubstantially parallel to said centerline of said hood mouth; saidcenterline of said reduced unrestricted portion being displaced from thecenterline of said hood mouth in the same direction as the centerline ofsaid furnace mouth when said furnace is rotated, the displacement ofsaid centerline of said reduced unrestricted portion being proportionalto the said angle whereby the face velocity of gas effluents enteringsaid hood through said reduced unrestricted portion is increased toimprove the gas effluent capture efficiency of said hood.

1. A device comprising: a. a rotatable metallurgical furnace having afurnace mouth disposed at its top; said furnace being disposed in anupright position for oxygen blowing operations and being adapted torotate about an axis to the left and to the right of said uprightposition for operations other than oxygen blowing operations; b. anexhaust hood positioned above said furnace for the capture of gaseffluent; said hood having a hood mouth that is aligned with saidfurnace mouth wheN said furnace is disposed in said upright position;and c. means for use at said hood mouth that is capable of variably andpartially restricting selected portions of the crosssectional area ofsaid hood mouth to provide a reduced, unrestricted portion and arestricted portion at said hood mouth; said means being cooperativelyassociated with the rotation of said furnace from its upright positionso that said reduced unrestricted portion is disposed to the left ofsaid restricted portion when said furnace is rotated to the left of saidupright position and said reduced unrestricted portion is disposed tothe right of said restricted portion when said furnace is rotated to theright of said upright position whereby the face velocity of gaseffluents entering said hood through said reduced unrestricted portionis increased to improve the capacity of said hood to capture gaseffluents.
 2. The device of claim 1 including means for synchronizingthe partial restriction of said hood mouth with the rotation of saidfurnace from its upright position.
 3. The device of claim 1 wherein saidmeans comprises a plate.
 4. The device of claim 3 wherein said plate isprotected from heat.
 5. The device of claim 3 wherein said plate iscooled with a fluid.
 6. The device of claim 3 wherein said plate iscooled with water.
 7. The device of claim 1 wherein said means isexternal of said hood.
 8. The device of claim 1 wherein said means iscapable of moving with respect to the thermal movement of said hood sothat the distance between said means and said hood is constantlymaintained.
 9. The device of claim 1 wherein said metallurgical furnaceis a basic oxygen furnace.
 10. The device of claim 1 wherein said meansis capable of partially restricting the cross-sectional area of saidhood mouth in proportion to the degree of rotation of said furnace fromits upright position.
 11. A device comprising: a. a rotatablemetallurgical furnace having a furnace mouth disposed at its top; saidfurnace capable of being disposed in an upright position for oxygenblowing operations and capable of being rotated about an axis in a planeof rotation in two opposed directions; b. an exhaust hood positionedabove said furnace having a hood mouth that is aligned with said planeof rotation of said furnace; c. means for use at said hood mouth whensaid furnace is rotated from its upright position that is capable ofvariably and partially restricting selected portions of thecross-sectional area of said hood mouth to provide a reducedunrestricted portion and a restricted portion at said hood mouth; saidreduced unrestricted portion being disposed in the same direction towhich said furnace mouth is rotated and said restricted portion beingdisposed in the opposite direction to which said furnace mouth isrotated, whereby the face velocity of gas effluents entering said hoodthrough said reduced unrestricted portion is increased to improve thecapacity of said hood to capture gas effluents.
 12. A device forimproving the gas effluent capture efficiency of an exhaust hood havinga hood mouth through which gas effluent is captured that iscooperatively associated with a rotatable metallurgical furnace having afurnace mouth; said hood mouth and said furnace mouth being capable ofalignment with each other and being capable of misalignment with eachother in two opposed directions of misalignment; said device comprising;Means for use at said hood mouth that is capable of variably andpartially restricting selected portions of the cross-sectional area ofsaid hood mouth to provide a reduced unrestricted portion and arestricted portion at said hood mouth and that is capable of providingsaid reduced unrestricted portion nearer said furnace mouth than saidrestricted portion when said furnace mouth is misaligned in eitherdirection if misalignment with said hood mouth whereby the face velocityof gas effluents passing through said reduced unrestricted porTion isincreased to improve the gas effluent capture efficiency of said hood.13. The device of claim 12 including means for synchronizing the partialrestriction of said hood mouth with the degree of misalignment of saidfurnace mouth and said hood mouth.
 14. The device of claim 12 whereinsaid means comprises: a. a pair of parallel tracks fixed adjacent tosaid hood lying in a common plane that extends adjacent to and beyondsaid hood mouth; b. a movable plate that is carried by said tracks; andc. means for moving said plate from a position remote from said hoodmouth to a position adjacent to said hood mouth in partial restrictionthereof.
 15. The device of claim 14 wherein said tracks carry means forprotecting said tracks from heat and molten metal.
 16. The device ofclaim 14 wherein said moving means comprises: a. a pair of motors eachof which is mounted on said plate at the sides thereof; and b. a drivewheel being carried by each of said tracks being rotatably fixed to eachof said motors for moving said closure plate along said tracks; each ofsaid motors being synchronized with each other.
 17. The device of claim14 wherein said driving means comprises: a. a motor situated at theremote end of and between said tracks; b. a drive axle cooperativelyassociated with said motor and extending between said tracks; c. a pairof first sprocket wheels one of which is mounted to one end of saiddrive axle and the other of which is mounted to the other end of saiddrive axle; d. a pair of second sprocket wheels disposed at the otheropposite end of said tracks, one of which is cooperatively associatedwith one of said first sprocket wheels and the other of which iscooperatively associated with the other of said first sprocket wheels.e. a pair of continuous chains engaging each pair of cooperating firstand second sprocket wheels; and, f. a pair of cog wheels fixed to eachside of said plate, one of which is cooperatively associated with one ofsaid continuous chains and the other of which is cooperativelyassociated with the other of said continuous chains.
 18. The device ofclaim 14 wherein said driving means comprises: a. two cylinders each ofwhich is pivotedly mounted to a frame at the remote end of said tracks;b. each cylinder carrying a plunger rod having its free end pivotedlymounted to said plate; and, c. means for activating said plunger rodsfor extension and retraction.
 19. The device of claim 14 includingexpansion mechanisms for moving said tracks with respect to said hoodmouth to accommodate the thermal expansion of said hood so that thedistance between said plate and said hood mouth is constantlymaintained.
 20. The device of claim 19 wherein said expansion mechanismscomprises: a. a cylinder secured to a frame; b. each cylinder having aplunger rod that is secured to said tracks; and c. means for activatingsaid plunger rods for extension and retraction.
 21. In an exhaust hoodhaving a hood mouth that cooperates with a rotatable metallurgicalfurnace having a furnace mouth and being adapted to rotate about an axisin a clockwise and a counter-clockwise direction; said hood mouth havinga centerline perpendicular to the plane in which said hood mouth liesand said furnace mouth having a centerline perpendicular to the plane inwhich said furnace mouth lies; said centerlines being coaxial when saidfurnace is disposed in a position for oxygen blowing operations and saidcenterlines intersecting each other at an angle when said furnace isrotated clockwise or counterclockwise, wherein the improvementcomprises: Means for use at said hood mouth that is capable of movinginto a position adjacent to said hood mouth that partially restricts thecross-sectional area of said hood mouth to provide a reducedunrestricted portion having a centerline that is perpendicular to theplane in which said reduced unrestricted portion lies and that issubstantially parallel to said centerline of said hood mouth; saidcenterline of said reduced unrestricted portion being displaced from thecenterline of said hood mouth in the same direction as the centerline ofsaid furnace mouth when said furnace is rotated, the displacement ofsaid centerline of said reduced unrestricted portion being proportionalto the said angle whereby the face velocity of gas effluents enteringsaid hood through said reduced unrestricted portion is increased toimprove the gas effluent capture efficiency of said hood.